The arrest comes almost a week after Acen King was gunned down in the back seat of his grandmother’s car.

The shooting sparked a community outcry, and police had offered a $40,000 reward for information leading to an arrest and conviction in the case.

The boy’s grandmother told police the incident began when a man in a car behind her at a stop sign started honking his horn, apparently upset she wasn’t moving quickly enough. The grandmother honked her horn, too.

Then, police said, the man got out of his black Chevrolet Impala and fired into her car.

“One shot was fired, and it went through the vehicle and hit the child,” said Lt. Steven McClanahan, Little Rock police spokesman.

Not realizing that the boy had been hit, the woman drove to a J.C. Penney about nine miles away. When she went to get him out of the car, she saw that her grandson was wounded, according to a police incident report.

“She didn’t know he was shot,” a bystander told the 911 operator after speaking with the grandmother. One of the callers, describing what happened to the 911 operator, said the grandmother feverishly performed CPR after the child sustained a neck wound.

The boy was transferred to the Arkansas Children’s Hospital, where he was pronounced dead. A 1-year-old child was also in the car at the time of the shooting, according to the police report.

Police said they believe the grandmother and the slain boy had no relationship with the gunman.